Surface film free active metal electrodes

IV. SURFACE FILM FREE ACTIVE METAL ELECTRODES... 

The most common active metal electrodes in nonaqueous systems are indeed the surface film controlled ones described above. However, there are some exceptional cases in which surface film free active electrodes in nonaqueous solutions can be obtained. Three types of such systems are blue solutions, aluminum nonaqueous-aprotic plating systems, and magnesium electrodes in Grignard reagent solutions. 

This process enables a surface film free active electrode to be obtained in a blue solution of solvated electrons. As explained by Peled [32], an equilibrium is reached at a certain concentration of the metal ions and electrons according to the following equation ... 

Gileadi et al. showed that it was possible to obtain aluminum ion-conducting nonpolar aprotic solutions [54-56]. Aromatic solvents such as toluene and ethylbenzene can dissolve AlBrj or AljBrg and LiBr or KBr, thus forming clusters of M+ AIBr4 or M+AljBr," (M+ is the alkali metal ion) which conduct ions by a hopping-type mechanism (in contrast to the ion transport via frictional motion in polar systems). In such solutions it is possible to plate aluminum and thus form a surface film s free active metal electrode in aprotic media (provided that the aprotic media are sufficiently pure and do not contain atmospheric and/or protic contaminants) [57],... 

In conclusion, there are still many unanswered questions regarding Mg deposition-dissolution processes in these systems that call for further work in this area. It is not at all clear whether Mg deposition in Grignard/ether systems occurs under surface film free conditions or whether there are mechanisms of ion transport (e.g., RMg+ or Mg2+) through surface films on Mg electrodes. It is not clear whether the native surface films on Mg electrodes dissolve in the Grignard solutions, allowing the interaction of a fresh Mg surface with the solution species (which may explain the high reversibility of the Mg electrode), or whether, even in this case, Mg dissolution occurs via the breakdown and repair of surface films (due to reaction of the active metal with solution species). 

Our work employs electrochemically initiated polymerization (EIP) which is an easy and flexible method to produce surface coatings of various kinds. The technique makes use of the decomposition of an electro-active initiator at an electrode to start a free-radical polymerization. The polymer is formed directly at the electrode surface. As a consequence, the films adhere tightly to the surface. Adhesion is based on physisorption of the hydrogel to the metal. Note in this context that EIP is different from electrografting of conductive polymers. In EIP, the initiator is the electro-active species, rather than the monomer. Recently, we reported on the formation of thermoresponsive poly-A -isopropylacrylamide (pNIPAm) hydrogel coatings on gold surfaces based on this approach. ... 

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